Forest fires are a recurrent ecological phenomenon in the Mediterranean basin. Nowadays, Europe is facing a new generation of particularly virulent wildfires of 5th generation that may induce severe molecular changes in soil organic matter (SOM) leading to immediate and long-term environmental consequences, these include the alteration of biogenic chemical structures and the accumulation of newly formed ones, enhancing dynamics in the complex balance between the different C-types[1,2]. The SOM is paramount as an indicator of soil health[1] and understanding SOM molecular composition, before and after the fire, is fundamental to monitoring changes in health status, as well as its natural or man-mediated recovery[2,3]. Here, we assess SOM molecular composition in severely fire-affected leptosols, at two depths (0–2 and 2–5 cm) under different vegetation types in SW Portugal (Aljezur, Algarve). The SOM characterization was conducted by analytical pyrolysis (Py-GC/MS), considered an appropriate technique for the structural characterization of complex organic matrices, providing also detailed structural information (fingerprinting) of individual compounds[3]. However, due to the relatively high number of chemical structures released by analytical pyrolysis, graphical-statistical methods, such as van Krevelen diagrams, were also applied to help monitor SOM molecular changes produced by fire[2,3]. This work represents the first attempt to evaluate the fire effects in SOM using a detailed molecular characterization of SOM under different vegetation canopies, recently affected by a 5th generation wildfire in southern Portugal. References [1] J.A. González-Pérez, F.J. González-Vila, et al., Environmental International, 30 (2004) 855–870. [2] N.T. Jiménez-Morillo, J.M. De la Rosa, et al., Catena, 145 (2016) 266–273. [3] N.T. Jiménez-Morillo, G. Almendros, et al., Science of the Total Environment, 728 (2020) 138715.

EROFIRE project (PCIF/RPG/0079/2018; FCT, Portugal), and MarkFire project (PAIDI2020, PY20_01073) co-funded by Junta de Andalucía and EU FEDER funds. This research was funded by the European Union through the European Regional Development Funds in the framework of the Interreg V A Spain-Portugal program (POCTEP) through the CILIFO (Ref.: 0753_CILIFO_5_E) and FIREPOCTEP (Ref.: 0756_FIREPOCTEP_6_E) project. A.Z.M. and N.T.J.M. thank the FCT for contracts CEECIND/01147/2017 and 2021/00711/CEECIND, respectively. A.Z.M. was also supported by MCIN Ramón y Cajal contract (RYC2019-026885-I).

Póster P-ENV-20 presentado en la XXI Reunión Científica de la Sociedad Española de Cromatografía y Técnicas Afines (SECyTA 2022) 25-27 octurbre 2022, Almería

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